• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권1호
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• pp.44-51
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• 2000

In this paper, using a wide-band AE sensor with the frequency range from 100[kHz] to 1.5[kHz], the frequency spectra of AE signals generated from the corona discharges of the needle-plane gap and from the partial discharges of an epoxy void were analyzed to determine the proper ultrasonic sensor with optimum frequency range according to the patterns of corona discharges. We also examined the propagation characteristics of AE signals in oil and the relationship between the magnitude of corona discharge and the magnitude of AE signals in peak-to-peak value under the application of 60[Hz] ac high-voltage. From these results, the main frequency spectra of AE signals emitted from the corona discharges of the needle-plane gap were about 130[kHz] by the fast fourier transform, but the main frequency spectra appeared to be 230[kHz] in the partial discharges of an epoxy void. The magnitude of AE signals was proportional to the magnitude of corona discharge and discharge current pulse with increasing the applied voltages.

• E2M - 전기 전자와 첨단 소재
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• 제8권4호
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• pp.458-463
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• 1995

The optical and electrical properties of $C_{22}$-Quinolinium(TCNQ) Langmuir-Blodgett films have been studied depending on the annealing temperatures. The optimal properties were investigated using UV/visible(300-800[nm]) absorption spectra and FTIR(Fourier-transformed- infrared) absorption measurements. The electrical properties were investigated in a frequency range of 10[Hz]-13[MHz]. The UV/visible absorption spectra at room temperature show that there are four characteristic peaks at 320, 380, 494 and 678[nm]. These absorption peaks decrease very rapidly above the annealing temperature of 180[.deg. C], which is due to a structural change of TCNQ. The FTIR absorption measurements strongly support the result of the UV/visible absorption spectra, because the absorption peak of TCNQ- at 2181[$cm^{-1}$ /] also decreases above 140[.deg. C]. The frequency-dependent dielectric constant shows that there is a dielectric dispersion near 1[MHz] which is due to an orientational polarization of the molecules inside the film. The overall frequency-dependent dielectric constant is higher near 80[.deg. C]. It may be due to a softness of the alkyl chains.s.

• Bulletin of the Korean Chemical Society
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• 제35권8호
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• pp.2512-2518
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• 2014

The praseodymium-doped $TiO_2$ photocatalyst samples, which could degrade methyl orange under UV irradiation, were prepared by sol-microwave method for improving the photocatalytic activity of $TiO_2$. The resulting materials were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, Fourier transform infrared spectra (FTIR) and Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS). It was found Pr doping retarded the growth of crystalline size and the phase transformation from anatase to rutile, and narrowed the band gap energy. Praseodymium doping brought about remarkable improvement in the photoactivity. The optimal dopant amount of Pr was 2% by molar of cement and the calcination temperature was $500^{\circ}C$ for the best photocatalytic activity. The improvement of photocatalytic activity was ascribed to the occurrence of lattice distortion and the effective containment of the recombination of the electron-hole by $Pr^{3+}$.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.18-25
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• 2005

Stochastic ground-motion method is adopted to simulate horizontal PGA values for the offshore Uljin earthquake recorded at nationwide seismic stations. For this purpose, the Fourier spectra are calculated at every stations based on comprehensive results of wave propagation and site effect which were previously revealed through inversion process applied to large accumulated spectral D/B. In addition, the apparent source spectrum of the offshore Uljin earthquake is estimated by removing the path and site response from the observed spectra. The distance dependent time-duration model is revised by iteratively fitting the PGA values generated by using the raw spectra data to the observed PGA data. The stochastic ground-motion method predicts the observed PGA values within a error of ${\sigma}_{log10}=0.1$. Transfer functions of a site relative to another site are estimated based on the error residual of the inversion results and used to convert PGA values at multiple stations to expected PGA values at a reference station of TJN. The converted PGA values can be used as basic data to evaluate the ground-motion attenuation relations developed for seismic hazard analysis that concerns the large damaging earthquakes.

• 천문학회지
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• 제34권1호
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• pp.1-8
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• 2001

We present a fast reduction method of survey data obtained using a single-dish radio telescope. Along with a brief review of classical method, a new method of identification and elimination of negative and positive bad channels are introduced using cloud identification code and several IRAF (Image Reduction and Analysis Facility) tasks relating statistics. Removing of several ripple patterns using Fourier Transform is also discussed. It is found that BACKGROUND task within IRAF is very efficient for fitting and subtraction of base-line with varying functions. Cloud identification method along with the possibility of its application for analysis of cloud structure is described, and future data reduction method is discussed.

• Journal of Photoscience
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• 제9권2호
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• pp.457-459
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• 2002

Sunlight causes various types of adverse skin changes on the sun-exposed areas of the skin, in which the most hazardous one is the induction of malignant skin tumours. FT -IR spectra were obtained from specimens excised from normal skin, BCCs, SCCs, MMs, nevi, lesions of solar keratosis and Bowen's disease. Tissue samples from freshly frozen specimens were cut into 2 sections in strictly sequential order to be stained with H & E for histopathological analysis, and then to be air-dried on CaF$_2$ slide glasses for further spectral data acquisition from defined area of interest. Intra- and inter-sample variations were estimated within grouped lesion categories according to each skin component. Mean spectra for each type of tissue pathology in the 800-1800 $cm^{-1}$ / region was interpreted using the classical group frequency approach that showed the most visible differences in spectra of benign, premalignant and malignant changes directly related to protein conformation and nucleic acid bases. The relative intensity of the nucleic acid peak was increased with progression to malignancy. In addition, PCA was able to evaluate and maximise the differences in the spectra by reducing the number of variables characterizing each patient and pathology category. This type of approach to non-destructively estimate the complexity of IR-spectra of inhomogeneous samples such as skin demonstrates the advantage of FT -IR microspectroscopy to be able to observe diseased states (benign, premalignant, malignant) and distinguish them from normal against a huge background of inter- and intra-subject variability.

• 대기
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• 제25권4호
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• pp.601-610
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• 2015

This study measured the emissivity spectra of 5 major rock-forming minerals using a Fourier Transform Infrared (FT-IR) spectrometer in the spectral region of $650{\sim}1400cm^{-1}$. The mineral samples are quartz, albite, bytownite, anorthite, and sandstone. We compared emissivity spectra measured in this study with spectra provided by Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Arizona State University (ASU). The spectral features of emissivity such as Reststrahlen Band (RB) and Christiansen Feature (CF) locations were compared. Results showed that both CF and RB locations of emissivity spectra measured in this study were similar to those from ASTER and ASU. In the case of quartz, the RB was occurred in the region of $700{\sim}850cm^{-1}$ and $1050{\sim}1250cm^{-1}$. The spectral position of emissivity peak was in good agreement with the location of ASTER and ASU. For plagioclase (albite, bytownite, and anorthite), the spectral location of CF was shifted toward larger wavenumber and the emissivity value was increased in the region of $870{\sim}1200cm^{-1}$ with Ca percentage. The CF of anorthite and bytownite was occurred at $1245.79cm^{-1}$, and that of albite was occurred at $1283.79cm^{-1}$. We also confirmed that emissivity feature of sandstone includes both emissivity features of quartz and calcite. However, there were some differences in the magnitude of emissivity and locations of RB and CF. These were due to the differences in measurement methods, and differences in particle size and temperature of samples.

• 한국지진공학회논문집
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• 제13권6호
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• pp.27-37
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• 2009

지진파의 푸리에 가속도스펙트럼(Fourier Acceleration Spectrum)에 기반한 계측진도 평가방법(Sokolov and Wald, 2002)의 국내 적용성을 평가하기 위해 관련 논문(연관희 등, 2009)에서 평가된 국내 지진의 진도 MMI ${leq}$ IV 범위에 대한 진도별 FAS 평균(m)과 표준편차(${\sigma}$) 모델을 이용하여, FAS 진도평가방법의 타당성을 평가하여 보았다. FAS 통계특성 모델 평가시 사용된 지진관측자 료의 FAS를 이용하고 본 연구에서 프로그램으로 구현된 FAS 진도평가기법을 적용할 경우 관측된 진도를 ${\sigma}$ = 0.74 MMI의 오차로 추정할 수 있었으며, 오차의 지진규모-거리 의존성을 추가로 보정할 경우 오차를 ${\sigma}$ = 0.61 MMI 까지도 저감할 수 있었다. 또한 본 방법을 MMI ${\leq}$ IV에 대한 국내 FAS 통계특성 모델과 MMI ${\geq}$ V에 대한 전 세계 FAS 통계특성 모델을 함께 이용하여, 진도 VI 이상인 국내 피해지진의 진도를 미소지진관측자료의 지진원특성을 이론적으로 증가시켜 도출된 스펙트럼을 이용하여 추정한 결과 최대 진도추정 오차 0.63 이내로 예측할 수 있었다.

• 조명전기설비학회논문지
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• 제18권2호
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• pp.36-43
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• 2004

본 연구에서는 운전중인 직류전동기의 브러시를 임의로 회전하여 브러시와 정류자편에 불꽃을 발생시켰을 때, 초음파센서와 AE센서를 이용하여 각각의 기계적 노이즈 신호를 검출하였으며, 이를 주파수 스펙트럼으로 분석하였다. 또한 직류전동기의 브러시가 중성축에 정상적으로 위치하여 운전하고 있을 때, 초음파센서와 AE센서를 이용하여 각각의 자기적 노이즈 신호를 검출하였으며, 이를 주파수 스펙트럼으로 분석하였다. 그리고 직류전동기의 브러시를 임의로 회전한 경우의 기계적 노이즈 신호 및 브러시가 중성축에 위치한 경우의 자기적 노이즈 신호를 비교ㆍ분석하였다. 실험 결과, 운전중인 직류전동기의 브러시를 회전방향으로 임의로 회전하여 검출한 초음파의 기계적 노이즈 신호는 브러시가 중성축에 정상적으로 위치하여 검출한 초음파의 자기적 노이즈 신호보다 대략 2.5∼3.0배 증가되었다. 또한 운전중인 직류전동기의 브러시를 회전방향으로 임의로 회전하여 불꽃을 발생시켰을 때, AE의 기계적 노이즈 신호를 검출하여 주파수 스펙트럼으로 분석한 결과 주된 주파수 영역이 대략 1.3[MHz]∼l.5[MHz]인 것으로 나타났다

• 한국정보통신학회논문지
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• 제24권11호
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• pp.1492-1499
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• 2020

기상 레이다 시스템은 일반적으로 강우 및 풍속 등과 관련된 기상 현상을 나타낸다. 이러한 시스템은 대부분의 경우 장거리용이며 비교적 높은 고도를 지향하고 있어 넓은 지역에서의 전체적인 기상 현상을 파악하는 목적으로는 매우 유용하다. 그러나 최근에 와서 국지적인 폭우나 또는 돌풍 등에 의한 재난현상이 빈번히 발생되고 있기 때문에 이러한 기상이변 현상의 탐지가 매우 중요한 문제이다. 국지적인 기상 이변 탐지목적의 기상 레이다는 저고도 탐지 및 급변하는 국지적인 기상상황의 빠른 탐지가 필요하다. 이러한 운용환경에서는 상대적으로 지표면 클러터가 큰 영향을 미치며 안테나의 신호 획득시간도 매우 짧아진다. 따라서 기존의 도플러 스펙트럼 추정방법에 심각한 문제가 발생할 수 있다. 본 논문에서는 이러한 문제점을 해결하기 위하여 AR(autoregressive) 도플러 스펙트럼 추정 방법들을 적용하고 결과들을 고찰하였다. 적용된 방법들을 이용하면 기존의 FFT(Fast Fourier Transform) 방법에 비하여 향상된 도플러 스펙트럼 추정이 가능함을 보였다.